280
FXUS66 KPQR 272109
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
209 PM PDT Sun Sep 27 2026

.SYNOPSIS...Dry weather continues through Monday with
temperatures near to slightly below seasonal average. A
weakening frontal boundary will bring the next chance for rain
Tuesday into early Wednesday, with the highest probabilities
along the coast, Coast Range, and northern Cascades while most
inland valleys remain dry. Dry weather is favored again for the
latter half of the week.

&&

.DISCUSSION...Now through Saturday...High pressure remains in
control across the region this afternoon, maintaining generally
quiet weather through Monday. A weak upper-level low is
settling southward toward California while low-level flow
gradually shifts from weak offshore flow today toward a light
onshore component Monday. Temperatures will remain seasonably
cool, with inland valley highs generally in the upper 60s to
possibly 70 on Monday.

Clear skies and light winds tonight will again promote efficient
radiational cooling, particularly in sheltered valleys. The
Upper Hood River Valley has the best potential for isolated
frost, with temperatures potentially falling into the mid to
upper 30s. However, the probability of temperatures dropping
below 36 degrees remains relatively low at around 10%. With
temperatures around 36 degrees this morning around Parkdale,
definitely will need to keep an eye on temperatures tonight
into Monday morning. Patchy morning fog is another possibility
where low-level moisture, light winds, and strong overnight
cooling overlap. The central and southern Willamette Valley,
Coast Range valleys, and Cascade valleys are among the more
favored locations. With that said, there is lower confidence for
fog tonight into Monday morning compared to previous mornings
as guidance has trended towards lower chances (10-20%). Any fog
that does form should remain localized and dissipate by late
morning Monday.

The next meaningful change arrives Tuesday as an upper-level
trough and weakening frontal boundary move into the Pacific
Northwest. Precipitation chances increase substantially along
the north Oregon Coast and Coast Range into southwest
Washington, with probabilities around 60-90% Tuesday afternoon
before gradually decreasing Tuesday night into Wednesday
morning. Some rain will likely extend into the northern Oregon
Cascades as well. Farther inland, confidence in measurable
rainfall remains much lower, with only around 5-25% of ensemble
members indicating more than a trace in the Portland metro and
Willamette Valley through Wednesday morning. However, just to
the north, there is a 45-70% chance of at least measurable
rainfall from Battle Ground to Longview. Most inland valley
locations should therefore remain dry, particularly farther
south.

The front weakens as it moves through the region, with dry
conditions expected to return by midday Wednesday and continue
through Thursday. Ensemble guidance remains split regarding the
upper-level pattern late next week, with roughly 35% of members
favoring weak troughing, 35% weak ridging, and 30% a more zonal
flow. The troughing scenario would bring cooler temperatures and
perhaps a few light coastal showers Thursday, while the ridging
and zonal solutions generally favor dry weather. Regardless of
the eventual result, the current range of outcomes suggests
relatively limited weather-related impacts through the end of
the week. ~12/99

&&

.AVIATION...Through 00Z Tuesday...VFR conditions prevail through
the TAF period with mostly clear skies. The only exception is a
30-50% chance of marine stratus along the far N OR and SW WA
coast, including KAST, between 12-19z Mon. North winds continue,
up to 10-15 kt along the coast with occasional gusts up to 20-25
kts by 19-21z Sun, remaining generally less than 10 kts inland.
Winds decrease by 06z Mon and remain light through the end of the
TAF period.

KPDX AND APPROACHES...VFR conditions are anticipated through
the TAF period. North to northwest winds around 8-10 kt,
decreasing after 04-06z Mon and remaining generally less than 5
kts through the rest of the period. -03

&&

.MARINE...Expect northerly winds to persist across the coastal
waters today thanks to lingering high pressure near the surface
helping to facilitate gusts up to 20-25 kts at times through this
evening. Small Craft Advisories remain in effect through 11 PM PT
Sunday. Wave heights will remain around 4-6 ft through tonight.

Then the focus shifts to a frontal boundary approaching the
waters on Monday, shifting winds more westerly during the daytime
hours then eventually southerly Monday evening. This frontal
feature finally moves through the waters the second half of
Tuesday. There are high chances (70-90%) of wind gusts exceeding
21 kts (Small Craft Advisory criteria) late Monday into Tuesday
for the coastal waters north of Cape Foulweather, with gusts most
likely peaking around 25-30 kts. Lighter northerly winds return
Tuesday night. A longer period west to northwesterly swell of 5-8
ft at 12-16 seconds will also move into the coastal waters late
Monday through Wednesday, resulting in a moderate sneaker wave
threat and increasing significant wave heights into the 6-9 ft
range. While seas gradually fall into Thursday, models hint at the
arrival of another WNW swell of similar magnitude around Friday.
-03

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory until 8 PM PDT this evening for PZZ210.

     Small Craft Advisory until 11 PM PDT this evening for PZZ251>253-
     271>273.
&&


$$

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